Fuente: Journal of applied polymer Lugar: RESEARCH ARTICLE Layered double hydroxide (LDH) attracts wide attention as eco-friendly flame retardant additives for PLA. Amino-tetrasulfide polysiloxane modified LDH achieves simultaneous enhancement of flame retardancy and interfacial compatibility in PLA composites. The composite reaches an LOI of 30.5% with UL-94 V-0 classification, and pyrolysis behaviors in gas and condensed phases are clarified.

ABSTRACT
Herein, a low-cost, easily operated strategy is proposed to improve the flame retardancy and interfacial adhesion of layered double hydroxides (LDHs) in polylactic acid (PLA) composites. Specifically, aminated polysiloxane containing tetrasulfide groups was grafted onto the surface of LDHs (denoted as KT-LDHs) by the condensation reaction. The results of detailed analysis showed that the surface of KT-LDHs was successfully coated polysiloxane with Si-S-N organic hybrid structure. It exhibited higher thermal stability than pristine LDHs within the melt processing temperature range of PLA. Owing to the presence of amino reactive groups and long alkyl chains on the surface, the interfacial adhesion between KT-LDHs and the PLA matrix was improved. Additionally, the PLA composite with 20 wt% of KT-LDHs could achieve a favorable UL-94 V-0 rating and a limiting oxygen index value of 30.5%. The formation of a dense char layer rich in Mg-Al-Si and the gaseous dilution/free radical quenching effect of elemental sulfur were considered to be the essential factors for reinforcing the flame retardancy of PLA. These were generated under the synergistic effect of LDHs and tetrasulfide polysiloxane with multiple flame-retardant mechanisms. Our strategy for LDHs modification overcomes the inherent limitations of single-component flame retardants and improves interfacial adhesion.